The present invention is generically directed on improvements with respect to so-called shower head gas inlet technique into a plasma discharge space of a plasma reactor operated with a plasma which is electrically fed by RF, RF plus DC or pulsed RF. Thereby, it is directed to parallel plate reactors, where RF energy is coupled to the discharge space via a pair of electrodes in a capacitance plate-like arrangement, in contrary to other reactors, where the discharge energy is introduced via microwave coupling or via induction field.
Such capacitive-coupling plasma reactors are commonly used for exposing at least one substrate at a time to the processing action of a plasma glow discharge. A wide variety of such processes are known and used to modify the nature of the substrate's surfaces. Depending on the process and in particular on the nature of gas injected in the glow discharge space of the reactor, one can modify the substrate's surface property, apply thin films thereto or remove, especially selectively remove, material therefrom.
The substrates can be plane or curved as e.g. car windshields. In such case the arrangement of the electrodes wherebetween the plasma discharge space is defined may be not coplanar, but accordingly curved in parallelism, so that the distance between the curved surface of the substrate and an electrode is substantially constant over the substrate's surface extent.
Although the present application claims for plasma reactors, it fully describes different inventive methods to manufacture substrates by means of process steps being performed by the claimed plasma reactor. Such manufacturing processes are especially directed on semiconductor wafers, disks for memory devices, flat display panels, window panes and web or foils.
The processes for surface treatment of substrates performed in a vacuum vessel, wherein a plasma discharge is generated with an RF component of electric field, are widely known as PVD, PECVD, as reactive ion etching, ion plating etc. processes.
In FIG. 1 there is schematically shown a commonly used design for an RF plasma reactor with a “shower head” gas inlet. A conventional RF plasma reactor comprises a reactor vessel 1 with a pumping port 3. Oppositely disposed, spaced metallic surfaces 4 and 6 are the plasma discharge electrodes and concomitantly define the plasma discharge space 8. Between the two electrode surfaces 4 and 6 the plasma discharge supplying electric field E at least with an RF component is applied.
At least one of the plasma discharge electrode surfaces 4, 6 is provided with a multitude of gas feed openings 10, the respective electrode being the surface of a plate 11. With respect to the plasma discharge space 8 on the backside of that plate 11 there is provided a reservoir chamber 12 with a back wall 14 and lateral rim wall 16. Centrally with respect to the extent of the reservoir chamber 12 there is provided a gas inlet opening and feed line 18. Besides of the gas feed openings 10 and opening 18 the reservoir chamber 12 is sealed.
The bordering metallic walls and plate enclosing the reservoir chamber 12 are fed with plasma discharge supplying electric energy as by a central electric feed line 20. As reactor vessel 1 is customarily not operated at the same electric potential as the electrode surface 4, especially not on full RF power, but is customarily operated at a reference potential as on ground potential, the overall reservoir chamber 12 is mounted within the reactor vessel 1 in an electrically isolated manner as schematically shown by an electrically isolating support and feed-through 22. The centrally disposed gas feed line 18 is analogously connected to a usually grounded gas supply line 24 to the reactor vessel 1 via an electrically isolating connector 26.
The gas feed openings 10 in electrode surface 4 and plate 11 of reservoir chamber 12 have a small gas conductance and, accordingly, a high gas flow resistance factor, so that the internal volume of reservoir chamber 12, centrally fed with inlet gas, acts as distributing and pressure equalisation chamber to feed gas through the gas feed openings 10 at a well-controlled and desired manner most often as homogeneously distributed as possible along the electrode surface 4 and into the plasma discharge space 8. As shown in FIG. 1 gas fed to the overall reactor is submitted to a large change of electric potential (pipe 24 to feed line 18). Thereby, the conditions in the area where this high potential difference occurs, i.e. at the connector 26, is quite critical for avoiding occurrence of unwanted plasma discharge therein.
A further drawback of this known arrangement is primarily its low response time. As the internal volume of the reservoir chamber 12 must be rather large to allow even gas distribution and constant pressure along plate 11, a rather large quantity of gas is accumulated in this reservoir chamber 12 at a relatively high pressure. Thus, if during processing one wants to change the gas composition or outflow rate, such change, considered in the plasma discharge space, will occur during a rather uncontrolled transient phase with large time constants up to reaching the desired stable, newly established gas composition and/or outflow rate.
Additionally, the volume of reservoir chamber 12 must be evacuated by vacuum pumping prior to starting a treatment process in the reactor, which takes the more time the larger the respective volume is construed. This especially considering the fact that the volume 12 is only connected to the pumping port of the vessel via small, low-conductance openings 10, so that pre-processing conditioning of the overall reactor, including degassing walls, takes a long time. Nevertheless and due to the low-conductance gas feed openings 10 and the large volume of reservoir chamber 12 this technique results in a satisfying control of gas outflow distribution along the electrode surface 4, as e.g. in a homogeneous distribution. By varying the density of gas feed openings 10 along the plasma discharge space bordering electrode surface 4 the gas distribution may easily be tailored according to specific needs.
It is a generic object of the present invention to improve a shower head RF reactor as principally shown in FIG. 1, thereby maintaining its advantages. We understand under the term RF reactor a reactor wherein plasma discharge is electrically supplied with at least an RF component of electric energy.
Under a first aspect of the present invention this object is resolved by an RF plasma reactor comprising a reactor vessel and therein a pair of electrodes consisting of spaced apart and oppositely disposed metallic surfaces defining therebetween a plasma discharge space, at least one of the metallic surfaces being the surface of a metallic plate having a multitude of gas feed openings therethrough and through the metallic surface towards the discharge space and from a distribution chamber extending along the plate opposite the discharge space, whereby the distribution chamber has a back wall opposite and distant from the plate and comprises a gas inlet arrangement with a multitude of gas inlet openings, which are distributed along the back wall and which are connected to at least one gas feed line to the reactor.
Thereby and in opposition to well-known techniques according to FIG. 1, gas inlet to the inventively provided distribution chamber is not performed locally, but via a multitude of gas inlet openings. This leads to the advantage that the requirements to the distribution chamber itself with respect to large volume pressure equalisation are significantly reduced compared with the teaching according to FIG. 1: The volume of the distribution chamber may be significantly reduced, which significantly improves response time when varying gas flow and/or gas composition to the plasma discharge space.
The above mentioned object is resolved under a second aspect of the present invention by an RF plasma reactor comprising a reactor vessel and therein a pair of electrodes consisting of spaced apart and oppositely disposed metallic surfaces defining therebetween a plasma discharge space, wherein at least one of the metallic surfaces is a surface of a metallic plate having a multitude of gas feed openings therethrough towards the discharge space and from a distribution chamber extending along the plate opposite to the discharge space, wherein the distribution chamber has a back wall opposite and distant from the plate with the gas inlet arrangement and further with an electric energy feed arrangement to the two metallic surfaces being the plasma discharge electrodes, and wherein further the back wall and the plate—substantially bordering the discharge space—are electrically isolated from each other. Thereby, any electrical potential difference, as especially the large plasma-supplying potential difference, may be applied between the plate and the back wall of the distribution chamber, so that the back wall may be directly part of the vessel's wall, driven on a desired electrical potential independent from the electric potential applied to the respective electrode surface, as e.g. operated at a reference potential, commonly on ground potential.
Thereby, on one hand the critical high potential difference along the gas feed line is avoided and is much easier to be handled across the distribution chamber. Further the overall construction of the reactor is significantly simplified as by avoiding electrically isolated suspension of the overall reservoir chamber in the reactor as is provided at 22 of the known technique according to FIG. 1
The above mentioned object is further resolved under a third aspect of the present invention by an RF plasma reactor comprising a reactor vessel and therein a pair of electrodes consisting of spaced apart and oppositely disposed metallic surfaces defining therebetween a plasma discharge space, at least one of the metallic surfaces being the surface of a metallic plate having a multitude of gas feed openings therethrough and through said metallic surface towards the discharge space and from a distribution chamber extending along the plate opposite the discharge space, whereby the distribution chamber has a back wall opposite and distant from the plate and comprises a gas inlet arrangement and wherein further at least one grid member is arranged within the distribution chamber distant from and along the plate and wherein the at least one grid member is electrically isolated from the back wall and from the plate.
We understand generically under the term grid a material structure of plate-like shape with perforations therethrough. Thus a grid may be realised by a more mesh-like structure up to a rigid plate with few perforations.
By subdividing the distribution space by means of such grid members—if of electroconductive material—in two or more than two sub-spaces, any electric potential difference between the plate and the back wall is subdivided to a fraction across each of the sub-spaces. This allows, with an eye on spurious plasma discharge formation in the distribution chamber, to the possibility of increasing the height of the sub-spaces and thus of the distribution chamber, considered perpendicularly to the plate, without incurring the risk of spurious plasma ignition. This is especially true if practically the complete plasma discharge potential difference is applied across the distribution chamber. In fact the spurious capacitance between the plate and the back wall bordering the distribution chamber is reduced. Additionally, provision of the grid member as mentioned improves gas pressure distribution and homogenisation along the distribution chamber, irrespective of whether the grid member is of electroconductive material or of dielectric material.
The generic object mentioned above is further resolved, under a fourth aspect of the present invention, by an RF plasma reactor comprising a reactor vessel and therein a pair of electrodes consisting of spaced apart and oppositely disposed metallic surfaces defining therebetween a plasma discharge space, at least one of the metallic surfaces being the surface of a metallic plate having a multitude of gas feed openings therethrough and through the metallic surface towards the discharge space and from a distribution chamber extending along the plate opposite the discharge space and wherein the distribution chamber has a back wall opposite and distant from the plate, and wherein further the wall comprises a lateral rim portion which extends towards and beyond the periphery of the plate and distant therefrom, and wherein the distribution chamber communicates by an opening arrangement with the interspace between the lateral rim portion of the wall and the periphery of the plate and said opening arrangement extends substantially parallel to the plates and substantially perpendicularly to the rim portion of the wall.
On one hand an additional amount of gas is fed to the plasma discharge space at its peripheral border area. As customarily more gas, in a reactive process more reactive gas is consumed at the periphery of the plasma discharge, this extra consumption is compensated. Thereby, the density of gas inlet openings per surface area in the plate and through the metallic electrode surface may not be increased indefinitely, as under consideration of technical efforts and manufacturing expenses, so that the peripheral gas feed as stated above is a most simple technique to increase the peripheral gas flow to the plasma discharge space.
It further must be considered that by the inventively provided rim portion of the wall, distant from the periphery of the plate, an inlet channel to the plasma discharge space is formed. If there is installed an electric potential difference between the plate and the wall, then this electric potential will also be present across said space from the periphery of the plate to the rim of the wall. Surprisingly, ignition of a spurious plasma discharge between rim and periphery of the plate is far less critical than e.g. in the gas feed openings in the plate or, generically spoken, in a “single potential” electrode environment.
In preferred embodiments the features of the four plasma reactors according to the present invention and following up their four aspects are inventively combined to further inventive plasma reactors, being the features of respective two of said reactors, three of said reactors or of all four of said reactors.
The invention under all its aspects will now be exemplified by means of figures and as far as necessary for the skilled artisan to understand the present invention even better under consideration of the description provided above. The further figures show:
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.